1. Field of the Invention
The invention relates to a compatible recording or reproduction device with three-point scanning for recording media having different track spacings.
2. Related Art
Optical and magnetic recording media having different track spacings are generally known. Recording media having a relatively small track spacing mainly belong to a more recent generation and, as a rule, permit the recording or the reproduction of larger volumes of information or data. In order also to be able to continue using recording media of an earlier generation, having a relatively large track spacing, in recording or reproduction devices of a more recent generation for recording media having a relatively small track spacing, these recording or reproduction devices must be compatible with the different recording media. It is desirable, for example, to be able to play CDs, too, in a recording or reproduction device for optical recording media having a high storage density, a so-called SD, which is also referred to as a Super Density disk. Compared with the CD, the SD has a higher storage density, which is achieved, inter alia, by a smaller track spacing. In order to be able to read both an SD and a CD in a recording or reproduction device, a compatible tracking system is therefore necessary. On account of the higher track density or the smaller track spacing in the case of the SD, the tracking of the SD with a generally known three-beam system is more critical than in the case of a CD. In a compatible recording or reproduction device which permits the playback both of a CD and of an SD using the same optical scanning system, it is therefore necessary to set the three-beam tracking in a manner such that it is optimal for the SD. This means that the beams provided for tracking, which are also referred to as the auxiliary beams E and F of the optical system, have to be adjusted in such a way that they are tangent to the SD track on both sides. As a result, the tracking on a CD using the three-beam system becomes more difficult since the auxiliary beams are imaged virtually completely on the CD track, which has a larger width. The amplitude and the phase spacing for tracking become smaller, with the result that the reproduction of a disk having high eccentricity cannot be ensured.
From EP 129 760, it is already known to match the spacing between the beams provided for tracking and the main light spot to the corresponding requirements by rotating the grating with which the auxiliary beams IF are produced. However, this necessitates control means, which require an additional outlay.